A HIERARCHICAL APPROACH TO REGIONAL FLOOD FREQUENCY ANALYSIS

A hierarchical approach to regional flood frequency estimation is described, where higher-order parameters controlling the skewness of annual maximum floods are determined from larger regions than are used for determining parameters controlling the coefficient of variation. Procedures based on two-component extreme value and generalized extreme value distributions are developed, and it is shown that dividing a region into subregions to estimate some parameters can lead to more precise quantile estimates. The practical problem of defining the optimum number of subregions is discussed.